In a recording/reproduction apparatus for optical disks, in order to read data from an optical disk or write data to an optical disk, it is necessary to access a desired position on the optical disk with an optical pickup. An optical pickup includes: a light source for emitting a light beam; an objective lens for converging the light beam onto an optical disk; and photosensitive elements for outputting electrical signals based on the light beam having been reflected from the optical disk.
A semiconductor laser is used as a light source in within the optical pickup. The semiconductor laser operates with a driving current which is supplied from the laser driving circuit, and is able to emit laser light at an intensity which is in accordance with the driving current.
If a portion of the laser light that has been reflected from the optical disk enters the semiconductor laser, the oscillation state of the laser is disturbed, thus resulting in problematic fluctuations of the intensity of laser light. Such fluctuations in laser light intensity that are caused by the returned light are referred to as “return light noise”. In order to reduce this return light noise, it is practiced to superpose a high-frequency signal on the driving current for the semiconductor laser so as to cause the semiconductor laser to oscillate in multi modes (high-frequency superposition).
In performing a high-frequency superposition, it has been proposed to employ impedance matching elements to reduce power loss of the high-frequency signal, thus realizing good signal reproduction characteristics (see, for example, Patent Document 1).
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2002-230812